A gasket is a material which is clamped between adjacent faces and acts as a static seal. Its use is prevalent in internal combustion engines wherein its primary functions are, first, to create a seal so that engine fluids, e.g., oils, fuels and coolants, within the engine cannot escape while at the same time to keep outside dirt and other contaminants from entering the engine (and other segments of the drive lines and associated components) and, second, to maintain this sealed condition during the service life of the engine. Depending upon its particular application, gasket materials may be required to resist extreme high and/or low temperatures, elevated pressures and/or vacuum, thermal expansion, high or low bolt torques, a variety of chemical compounds and severe environmental conditions. To accomplish these many and varied tasks a wide selection of materials have been employed over the years for gasketing purposes including cork, paper, metal, plastics, natural and synthetic elastomers and various fibrous materials, such as asbestos, mineral, cellulose and polymer.
Gasketing materials for use in internal combustion engine applications involving prolonged exposure to hot oils, and other hydrocarbon fluids must, in addition to exhibiting acceptable oil aging characteristics be temperature, pressure and chemical resistant and possess adequate strength properties such as compressibility and crush resistance. It is frequently desirable that such gasketing materials swell when exposed to hot oil to provide improved sealing even under low compressive loads. Such materials typically comprise elastomeric bonded fibrous compositions and find utility in such applications as head gaskets, valve cover gaskets, rocker housing gaskets, oil pan gaskets, front cover gaskets, water pump and other coolant system gaskets and fuel pump and other fuel system gaskets. The fibrous portion of the composition imparts strength; the elastomeric component gives it resilience and conformability. Notwithstanding that gasket manufacturers may select the elastomeric binder from a wide variety of natural and synthetic rubbers which are commonly in use and exhibit at least some of the desired characteristics, none display all of these properties, particularly resistance to oil degradation over a prolonged period of time. Currently available and commonly used high swell gasket materials use natural and/or SBR rubber binders, both of which swell but also severely degrade upon prolonged exposure to hot oil.
New concepts in internal combustion engine design, resulting, for example, in low flange loads, have made it very difficult to obtain a sealed joint without utilizing either a high swell gasket composition or elastomeric stress risers on a nonswelling gasket material. Experience has shown that upon prolonged exposure to hydrocarbon oil containing engine fluids, such as lubricating oil, diesel fuel, and the like, currently available high swell gasket materials eventually degrade resulting in high mileage failures. A similar problem exists with elastomeric stress risers which also exhibit severe degradation when continuously exposed to hydrocarbon oil containing engine fluids.
It is, therefore, the purpose of the present invention to overcome previously encountered problems and to provide a high swell gasket composition which swells in contact with hydrocarbon oil containing engine fluids in order to provide a seal even under low flange loading but which does not degrade upon prolonged exposure to such fluids. Desirably, such a gasket composition, in addition, holds up well under either high or low temperature conditions and exhibits high compressive strength, e.g., is crush resistant, to avoid extruding when subjected to high loading.